Sleep is generally beneficial and restorative to a patient, exerting great influence on the quality of life. As a person falls asleep, brain activity declines and there is a progressive increase in the depth of sleep. A typical night's sleep for a normal person quickly transitions to a sleep stage known as slow wave sleep (SWS) characterized by low frequency electroencephalogram (EEG) activity. At approximately ninety minute intervals, sleep lightens and a sleep state known as rapid eye movement (REM) sleep is initiated. REM sleep is characterized by high frequency EEG activity, bursts of rapid eye movements, skeletal muscle atonia, and heightened autonomic activity.
There are typically 4-6 REM periods per night, with increasing duration and intensity toward morning. While dreams can occur during either REM or SWS sleep, the nature of the dreams varies depending on the type of sleep. REM sleep dreams tend to be more vivid and emotionally intense than SWS sleep dreams. Furthermore, autonomic nervous system activity is dramatically altered when REM sleep is initiated.
In patients with respiratory or heart disease, the brain during sleep can precipitate breathing disturbances, myocardial ischemia, or arrhythmia. Although REM sleep is a necessary component of normal sleep, serious consequences may be associated with both the increase in autonomic activity and the intense emotional responses that accompany dreaming in patients with cardiovascular or respiratory disease. Knowledge of the patient's sleep state may be used to enhance diagnosis and/or treatment of various disorders.